This invention relates to line protectors for communications circuits, more particularly to line protectors comprising gas-filled tubes.
Gas-filled tubes of the foregoing type are generally known and are used to protect telephone lines and related equipment in communications circuits. In one mode of operation high voltage transients across the protected line causes an arc gap betwen the electrodes resulting in a current discharge to ground. Under these conditions the unit is self-restoring, i.e., nothing need to be done in order to reset the unit for further operation. However, if a current in the circuit between the electrodes causes the gas tube to be placed in a so-called "glow mode," the resistance caused by the discharge across the gap results in a rise in temperature while the current is still flowing. Under these conditions the gas tube "glows", i.e., becomes hot and may tend to fail causing an open circuit condition. This can result in damage to the equipment or possibly a fire.
According to the present invention, an arrangement is provided for establishing a direct metallic short circuit from line to ground, bypassing the electrodes, when the gas tube becomes sufficiently overheated as a result of excessive current flowing therethrough.